Ultrasonic NDE and SHM methods serve as one of the primary maintenance techniques to ensure the safe operations of various mechanical structures, such as aircraft structures, pipelines, ships, and railways. With reliable defect detection capabilities, ultrasonic NDE and SHM methods are extensively used in the field to determine whether the inspected structures need to be repaired or replaced to ensure structural safety.
In ultrasonic NDE and SHM, quite often it is encountered some inspection objects, whose material properties and accurate dimensions are unknown due to poor records, material degradations, or other reasons. Conventional ultrasonic inspection techniques are problematic because the inspections rely on the ultrasonic wave speeds that are usually calculated from the material properties. For structures with material anisotropies, for instance, fiber-reinforced composite structures, it is also critical to know the direction dependence of the wave speeds. Furthermore, ultrasonic guided wave inspection techniques usually require the generation of guided wave dispersion curves based on the material properties as well as the geometries of the structures to be inspected. Dispersion curves not only serve as guidelines for selecting the parameters of the transducers that are suitable for the ultrasonic inspections, but also play an important role in determining the defect locations. When applying conventional ultrasonic guided wave techniques to inspect anisotropic structures, the directionally dependant dispersion curves and the direction of anisotropy need to be known. Similar requirements on the knowledge of wave velocities from the material properties and structure geometries are applied to passive acoustic emission tests, in which the location of the acoustic emission source, i.e., the defect location, is determined on the basis of the time-of-flights (TOFs) of the acoustic emission signals and the corresponding wave speeds. Consequently, conventional systems and methods do not allow for the inspection of materials having unknown properties such as the direction of anisotropy.
Accordingly, a system and method for inspecting a material having unknown properties is desirable.